System and method for drilling multilateral wells using magnetic ranging while drilling

ABSTRACT

Systems and methods for drilling a multilateral well using magnetic ranging while drilling are provided. In accordance with one embodiment, a method of drilling a multilateral well includes drilling and casing a mother wellbore, installing a multilateral junction, drilling and casing a first lateral well from the multilateral junction, and drilling a second lateral well from the multilateral junction using magnetic ranging while drilling such that the second lateral well has a controlled relationship relative to the first lateral well. The first and second lateral wells may form a SAGD well pair, in which case the first lateral well may be a producer well and the second lateral well may be an injector well.

BACKGROUND OF THE INVENTION

The present invention relates generally to well drilling operations and,more particularly, to well drilling operations using magnetic ranging todrill multilateral wells.

Heavy oil is too viscous in its natural state to be produced from aconventional well. To produce heavy oil, a pair of Steam AssistedGravity Drainage (SAGD) wells may be employed, which use superheatedsteam to heat heavy oil until its viscosity is low enough to beproduced. A SAGD well pair includes two parallel horizontal wells whichgenerally remain separated by an approximately constant verticalseparation distance (e.g., 4 to 6 m) over a horizontal distance ofroughly 500 m to 1500 m.

The upper well in a SAGD well pair is known as an “injector well.” Theinjector well injects superheated steam into a heavy oil zone formation,creating a steam chamber to heat the heavy oil contained therewithin.The lower well in a SAGD well pair is known as a “producer well.” Whenthe heated heavy oil becomes less viscous, gravity pulls the oil intothe producer well below, from which the oil may be extracted.

Conventional measurement while drilling (MWD) survey data does notprovide sufficient accuracy to maintain a consistent separation distancebetween the injector well and the producer well. Instead, conventionalmagnetic ranging may be employed to drill the second of the two wells ofa SAGD well pair. With conventional magnetic ranging techniques, awireline tool is placed in the first well while the second well isdrilled. A magnetic field between the wireline tool in the first welland a bottom hole assembly (BHA) in the second well allows the BHA inthe second well to maintain an accurate vertical separation distancebetween the first and second wells of the SAGD pair.

To reduce environmental impact at the surface, and for economic reasons,many non-SAGD wells employ a single mother wellbore having one or moremultilateral junctions. The multilateral junctions allow multiplelateral wells to extend from the mother wellbore beneath the surface,which may increase oil recovery while reducing costs. However,multilateral junctions cannot be used with SAGD wells drilled usingconventional magnetic ranging techniques. Since conventional magneticranging techniques involve placing a wireline tool into the first wellof a SAGD well pair while the second well is drilled, the wirelineassociated with the wireline tool would be present alongside the drillpipe in the mother well. As such, the wireline could become wrappedaround or crushed by the drill pipe, and cuttings from the second wellcould enter the first well and trap the wireline tool.

SUMMARY

Certain aspects commensurate in scope with the originally claimedinvention are set forth below. It should be understood that theseaspects are presented merely to provide the reader with a brief summaryof certain forms the invention might take and that these aspects are notintended to limit the scope of the invention. Indeed, the invention mayencompass a variety of aspects that may not be set forth below.

In accordance with one embodiment of the invention, a method of drillinga multilateral well includes drilling and casing a mother wellbore,installing a multilateral junction, drilling and casing a first lateralwell from the multilateral junction, and drilling a second lateral wellfrom the multilateral junction using magnetic ranging while drillingsuch that the second lateral well has a controlled relationship relativeto the first lateral well. The first and second lateral wells may form aSAGD well pair, in which case the first lateral well may be a producerwell and the second lateral well may be an injector well.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1 is a schematic diagram depicting a multilateral well drillingoperation in accordance with one embodiment of the invention;

FIG. 2 is a schematic diagram illustrating the use of magnetic rangingwhile drilling in the multilateral well drilling operations of FIG. 1;

FIG. 3 is a schematic diagram depicting a completed multilateral welldrilled using the multilateral well drilling operation of FIG. 1;

FIG. 4 is a schematic diagram depicting a completed multilateral welldrilled using the multilateral well drilling operations of FIG. 1 havingan in-well steam generator in accordance with another embodiment of theinvention;

FIG. 5 is a flowchart describing a method of performing the multilateralwell drilling operation of FIG. 1;

FIG. 6 is a schematic diagram depicting a multilateral well havingmultiple multilateral well pairs drilled in accordance with oneembodiment of the invention;

FIG. 7 is a flowchart describing a method of drilling the multilateralwell of FIG. 6;

FIG. 8 is a schematic diagram depicting a pair of fishbone wells drilledin accordance with one embodiment of the invention; and

FIG. 9 is a flowchart depicting a method of drilling the pair offishbone wells depicted in FIG. 8.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention are describedbelow. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

FIG. 1 depicts a well drilling operation 10 involving drilling amultilateral well using magnetic ranging while drilling. A motherwellbore 12 extends through a formation 14 into a heavy oil zoneformation 16. A multilateral junction 18 allows a Steam Assisted GravityDrainage (SAGD) well pair, which includes a producer well 20 and aninjector well 22, to branch from the mother wellbore 12 at the base ofthe heavy oil zone formation 16.

In the well drilling operation 10 of FIG. 1, the producer well 20 hasbeen drilled and cased with slotted liner 24, which allows oil to enterthe producer well 20 while protecting the producer well 20 fromcollapse. To drill the injector well 22, a whip stock and packer 26 hasbeen inserted into the multilateral junction 18 at the site of themultilateral junction 18. The whip stock and packer 26 guide a drillpipe 28 having a bottom hole assembly (BHA) 30 through the multilateraljunction 18 away from the mother wellbore 12. Additionally, as cuttingsfrom the injector well 22 are circulated out, the whipstock and packer26 prevent the cuttings from falling into the producer well 20.

The BHA 30 includes a drill bit 32 for drilling through the heavy oilzone formation 16 and a steerable system 34 to set the direction of thedrill bit 32. The BHA 30 includes an electric current driving tool 36,which may be a component of a measurement while drilling (MWD) tool or astandalone tool, such as Schlumberger's E-Pulse™ or E-Pulse Express™tool. The electric current driving tool 36 provides an electric currentto an outer drill collar 38 of the BHA 30. The outer drill collar 38 isseparated from the rest of the drill pipe 28 by an insulated gap 40 inthe drill collar, through which electric current may not pass. The BHA30 additionally includes a magnetometer tool 42 having a three-axismagnetometer 44. The three-axis magnetometer 44 is employed in atechnique known as magnetic ranging while drilling, which is describedbelow. It should be noted that the BHA 30 may also include logging whiledrilling (LWD) tools, telemetry tools, and/or other downhole tools foruse in a drilling environment.

Turning to FIG. 2, a schematic of well drilling operation 46 illustratesthe use of magnetic ranging while drilling to drill the injector well 22at an approximately constant vertical separation distance from theproducer well 20 in accordance with exemplary embodiments of the presentinvention. Without need for a separate wireline tool, magnetic rangingwhile drilling allows the BHA 30 to maintain a precise distance from thepreviously cased producer well 20. Though an overview of magneticranging while drilling is discussed below, a detailed description ofmagnetic ranging while drilling is available in published application US2007/016426 A1, assigned to Schlumberger Technology Corporation, whichis incorporated herein by reference.

To ascertain a vertical separation distance from the producer well 20using magnetic ranging while drilling, the electric current driving tool36 first provides an electric current 48 to the outer drill collar 38.The current 48 produced by the electric current driving tool 36 may, forexample, have a frequency between about 1 Hz and about 100 Hz, and mayhave an amplitude of around 17 amps. Beginning along the outer drillcollar 38 of the BHA 30, the current 48 may subsequently enter the heavyoil zone formation 16. The portion of the current 48 that enters theheavy oil zone formation 16 is depicted as an electric current 50.

The slotted liner 24 of the producer well 20 provides very lowresistance to electricity as compared to the heavy oil zone formation16, being typically six orders of magnitude lower than the resistance ofthe heavy oil zone formation 16. As a result, a substantial portion ofthe current 50 will pass along the slotted liner 24, depicted as acurrent 52, rather than travel elsewhere through the heavy oil zoneformation 16. The current 52 travels along the slotted liner 24 beforere-entering the heavy oil zone formation as current 54 on its way towardcompleting the circuit beginning at the electric current driving tool36, located on the opposite side of the insulated gap 40 from the startof current 48.

The movement of the current 52 along the slotted liner 24 creates amagnetic field 56, an azimuthal magnetic field centered on the slottedliner 24. The three-axis magnetometer 44 of the magnetometer tool 42 maydetect both the magnitude and the direction of the magnetic field 56along three axes. The magnitude and direction of the magnetic field 56may be used to estimate the direction and distance from the BHA 30 ofthe producer well 20. Having determined the direction and distance fromthe producer well 20, the BHA 30 may be controlled to drill the injectorwell 22 at an approximately constant separation distance 58 from theproducer well 20 over the entire length of the producer well 20 and theinjector well 22. For example, the precision available with magneticranging while drilling may permit a controlled relationship between theproducer well 20 and the injector well 22, such that the approximatelyconstant separation distance 58 approaches five meters (5 m) with avariance of approximately one meter (1 m) (i.e., a separation distanceof 4-6 meters (m) along the entire length of the producer well 20).

FIG. 3 depicts a completed multilateral SAGD well 60. In the completedmultilateral SAGD well 60, the producer well 20 is cased with slottedliner 24, which allows oil to enter the producer well 20 whileprotecting the producer well 20 from collapse. The injector well 22,located directly above and parallel to the producer well at theapproximately constant separation distance 58, is cased with slottedliner 62 to permit steam to exit the injector well 22 while protectingthe injector well 22 from collapse. It should be appreciated thatslotted liner may not be the only form of casing that is used on theproducer well 20 and the injector well 22. The completed multilateralSAGD well 60 may also include producer tubing 64 and injector tubing 66.The producer tubing 64 is used to transport heavy oil that enters theproducer well 20 up to the surface, and the injector tubing 66 isconfigured to carry steam generated at the surface down into injectorwell 22.

The mother wellbore 12 may have casing with thermal insulation 68. Theinsulation 68 reduces the amount of heat loss to the formations 14 and16 from steam traveling from the surface toward the injector well 22through the injector tubing 66. Additionally, the insulation 68 may alsoreduce the amount of heat loss to the formations 14 and 16 by the heatedheavy oil in the producer tubing 64. Since heavy oil grows substantiallymore viscous as it cools, preventing the produced heavy oil from coolingmay reduce lifting costs incurred to lift more viscous oil.

It should also be noted that by using a single mother wellbore 12, thecompleted multilateral SAGD well 60 may have a reduced footprint andenvironmental impact. In certain regions, such as arctic regions likeAlaska, a large number of well penetrations at the surface could damagethe permafrost. Moreover, significant heat could be lost as steam isdelivered to depths which may approach more than one thousand feet, andthe produced oil in producer tubing 64 could have cooled, increasinglifting costs resulting from increased viscosity. Since the completedmultilateral SAGD well has only a single mother wellbore 12, the surfacearea of the casing that is exposed to the surrounding formations 14 and16 is minimized, reducing the total likely heat loss. Further, thermalinsulation may be more cost-effective than with conventional SAGD wells,as only the mother wellbore 12 is insulated instead of than twoconventional wells.

FIG. 4 depicts a completed multilateral SAGD well 70, completed in asimilar fashion to the completed multilateral SAGD well 60, butconfigured to generate steam for the injector well 22 downhole inaccordance with another embodiment of the present invention. In thecompleted multilateral SAGD well 70, as in the completed multilateralSAGD well 60 above, the producer well 20 is cased with slotted liner 24,which allows oil to enter the producer well 20 while protecting theproducer well 20 from collapse. The injector well 22, located directlyabove and parallel to the producer well at the approximately constantseparation distance 58, is cased with slotted liner 62 to permit steamto exit the injector well 22 while protecting the injector well 22 fromcollapse. The completed multilateral SAGD well 70 may also includeproducer tubing 64, which is used to transport heavy oil that enters theproducer well 20 up to the surface.

Rather than employ injector tubing to transport steam generated at thesurface into the injector well, the completed multilateral SAGD well 70generates steam in the injector well at the base of the mother wellbore12. Steam generation tubing 72, which includes tubing for oxygen, fueland water, may supply a steam generator 74. The steam generator 74 maythen produce the steam necessary to perform SAGD production operationsat the injector well 22.

Turning to FIG. 5, a flow chart 76 depicts a method of drilling themultilateral wells depicted in FIGS. 1-4. In a first step 78, the motherwellbore 12 is drilled down into the heavy oil zone 16. Subsequently,the mother wellbore 12 is cased. In step 80, a multilateral junction 18is installed. The multilateral junction 18 may be any appropriatemultilateral junction, but may most likely be a level 5 or a level 6multilateral junction. Such multilateral junctions may includeSchlumberger's RapidX™ or RapidSeal™ multilateral junctions. In step 82,the horizontal producer well 20 is drilled near the base of the heavyoil zone 16. In step 84, the slotted liner 24 is installed in theproducer well 20.

To begin drilling the injector well 22, in step 86, the whipstock andpacker 26 are set in the multilateral junction 18. In step 88, theinjector well 22 is drilled as the BHA 30 and drill pipe 28 are guidedby the whipstock and packer 26 through the multilateral junction 18. Theinjector well is drilled maintaining a correct distance above theproducer well 20 using magnetic ranging while drilling. Thus, withmagnetic ranging while drilling, an approximately constant separationdistance 58 may be maintained between the parallel producer well 20 andthe injector well 22. In step 90, the injector well 22 is cased withslotted liner 62. In step 92 the whipstock and packer 26 is removed andthe remaining completions are run, resulting in the completedmultilateral SAGD well 60 or the completed multilateral SAGD well 70.

FIG. 6 depicts a completed multilateral SAGD well 94, in which aplurality of multilateral SAGD wells share a single mother wellbore 126.In the completed multilateral SAGD well 94, a plurality of multilateraljunctions 96, 98, and 100 may be installed near the base of the motherwellbore. It should be noted, however, that any number of multilateraljunctions may be employed as necessary to achieve a desired multilateralSAGD well configuration.

The completed multilateral SAGD well 94 includes two producer wells 102and 104 and two parallel injector wells 106 and 108. Producer well 102is cased with slotted liner 110 and completed with producer tubing 112,and producer well 104 is cased with slotted liner 114 and completed withproducer tubing 116. Similarly, injector well 106 is cased with slottedliner 118 and completed with injector tubing 120, and injector well 108is cased with slotted liner 122 and completed with injector tubing 124.It should be appreciated, as noted above, that slotted liner may not bethe only form of casing that is used on the producer wells 102 and 104and the injector wells 106 and 108.

The mother wellbore 126 extends from the surface through the formation14 into the heavy oil zone 16. To prevent unnecessary heat loss, themother wellbore 126 may be insulated with insulation 128. As in thecompleted multilateral wells 60 and 70, the insulation 128 serves toreduce the amount of heat loss to the formations 14 and 16 from steamtraveling from the surface to the injector wells 106 and 108 through theinjector tubing 120 and 124. The insulation 128 may also reduce theamount of heat loss to the formations 14 and 16 by the heated heavy oilin the producer tubing 112 and 116. Additionally, because fewer wellswill need to be drilled from the surface, the footprint andenvironmental impact of the completed multilateral SAGD well 94 may bereduced.

It should be appreciated that the completed multilateral SAGD well 94may be modified to generate steam downhole, rather than at the surface,in a similar manner to that of the completed multilateral well 70 ofFIG. 4. In such an embodiment, steam generation tubing for oxygen, fuel,and water may supply a downhole steam generator. The steam generator maythen produce the steam for injection into the injector wells 106 and108.

FIG. 7 depicts a flow chart 130 for drilling the completed multilateralSAGD well 94 of FIG. 6. In step 132, the mother wellbore 126 is drilledthrough the formation 14 into the heavy oil zone 16. In step 134, one ormore multilateral junctions 96, 98 or 100 may be installed to achieve adesired multilateral configuration. The multilateral junctions 96, 98and 100 may be any appropriate multilateral junctions, but may mostlikely be level 5 or level 6 multilateral junctions. Such multilateraljunctions may include Schlumberger's RapidX™ or RapidSeal™ multilateraljunctions.

Once the multilateral junctions 96, 98 or 100 are installed, theproducer wells 102 and 104 are drilled and cased with slotted liner 110and 114 near the base of the heavy oil zone 16 in step 136. With theproducer wells 102 and 104 drilled and cased, the corresponding injectorwells 106 and 108 may be drilled. In step 138, a whipstock and packermay be set for the first injector well 106. The first injector well 106is drilled in step 140, employing magnetic ranging while drilling tomaintain an approximately constant distance of separation between theinjector well 106 and the producer well 102, using the techniquesdiscussed above. In step 142, the slotted liner 110 is run in the firstinjector well 106.

To begin drilling the second injector well 108, the whipstock and packermay be removed from the first multilateral junction 96 and reset in step144. In step 146, the second injector well 108 is drilled, employingmagnetic ranging while drilling to maintain an approximately constantdistance of separation between the injector well 108 and the producerwell 104. After the slotted liner 122 is run in the second injector wellin step 148, the whipstock and packer may be removed. In step 150, theremainder of the completions is run.

FIG. 8 illustrates a SAGD fishbone well pair 152 which has been drilledusing magnetic ranging while drilling. The SAGD fishbone well pair 152includes a fishbone producer well 154 and a fishbone injector well 156.The fishbone producer well 154 includes a plurality of multilateralinjunctions 158, providing branches for a plurality of lateral producerwells 160. Similarly, the fishbone injector well 156 includes aplurality of multilateral junctions 162 placed respectively above themultilateral junctions 158 of the fishbone producer well 154. Havingsuch placement, a plurality of lateral injector wells 164 may be drilleddirectly above the lateral producer wells 160 at an approximatelyconstant separation distance.

Provided that the fishbone producer well 154 has been cased with aconductive liner, the lateral injector wells 164 may each be drilledemploying magnetic ranging while drilling to maintain an approximatelyconstant separation distance above the respective lateral producer wells160. It should be further noted that magnetic ranging while drilling mayalso be employed in drilling a vertical producer mother wellbore 166parallel to a vertical injector mother wellbore 168 through theformation 14 into the heavy oil zone 16.

It should be appreciated that the fishbone injector well 156 may bemodified to generate steam downhole, rather than at the surface, in asimilar manner to that of the completed multilateral well 70 of FIG. 4.In such an embodiment, steam generation tubing for oxygen, fuel, andwater may supply a downhole steam generator. The steam generator maythen produce the steam for injection into the lateral injector wells164.

Turning to FIG. 9, a flow chart 170 illustrates a method of drilling theSAGD fishbone well pair 152 of FIG. 8. In step 172, the producer motherwellbore 166 is drilled down to the heavy oil zone 16, the plurality ofmultilateral junctions 158 is installed, and the lateral producer wells160 are drilled. In step 174, the fishbone producer well 154 is cased inslotted liner. Additional completions may also be run, but may not benecessary at this time.

In step 176, the fishbone injector well 156 is drilled. Employingmagnetic ranging while drilling, the horizontal portion of the injectormother wellbore 168 may be drilled at an approximately constantseparation distance above the fishbone producer well 154. At eachmultilateral junction 162, corresponding respectively to multilateraljunctions 158, the lateral injector wells 164 are drilled with magneticranging while drilling directly above the lateral producer wells 160. Instep 178, the fishbone injector well 156 may be cased in slotted linerand completion subsequently run.

It should be appreciated that the above-discussed multilateral wells mayinclude a number of modifications or variations, such that one lateralwellbore is spaced accurately apart from another respective wellbore.For example, any of the disclosed embodiments may additionally oralternatively include a parallel horizontal monitoring well drilled atan approximately constant horizontal, rather than vertical, separationdistance. Moreover, the embodiments may be modified to accommodate VAPEXor ES-SAGD oil production techniques. The wells may also be completedwith casing or liners, and be slotted or solid. Electric heaters,radio-frequency heaters, induction heaters or other heating means may beused in place of steam. Furthermore, parallel wells may be drilled froma mother borehole using multilateral junctions for producingconventional oil or natural gas, the parallel well bores being used formonitoring production, or injecting gas or water to aid production.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A method for drilling a multilateral well comprising: drilling andcasing a mother wellbore; installing a multilateral junction in themother wellbore; drilling and casing a first lateral well from themultilateral junction, wherein the first multilateral well has a length;and drilling a second lateral well from the multilateral junction usingmagnetic ranging while drilling such that the second lateral well has acontrolled relationship relative to the first lateral well.
 2. Themethod of claim 1, wherein the controlled relationship is anapproximately constant distance and spatial relationship.
 3. The methodof claim 2, wherein drilling and casing the first lateral well comprisesdrilling and casing a producer well, and wherein drilling the secondlateral well comprises drilling an injector well.
 4. The method of claim3, comprising installing a steam generator in the injector well.
 5. Themethod of claim 2, wherein drilling the second lateral well comprisesdrilling the second lateral well such that the separation distance ofthe second lateral well relative to the first lateral well varies byless than or equal to 20% along the entire length of the first lateralwell.
 6. The method of claim 5, wherein drilling the second lateral wellcomprises drilling the second lateral well such that the separationdistance of the second lateral well relative to the first lateral wellis within a range of 4-6 meters along the entire length of the firstlateral well.
 7. The method of claim 1, wherein drilling the secondlateral well comprises drilling the second lateral well such that thesecond lateral well is directly above the first lateral well.
 8. Themethod of claim 1, comprising setting a whipstock in the multilateraljunction after drilling and casing the first lateral well and beforedrilling the second lateral well.
 9. The method of claim 1, whereindrilling the second lateral well comprises drilling the second lateralwell such that the second lateral well is in the same horizontal planeas the first lateral well.
 10. The method of claim 1, wherein drillingthe second lateral well comprises drilling the second lateral well suchthat the second lateral well is in the same vertical plane as the firstlateral well.
 11. The method of claim 1, wherein the method is performedin the recited order.
 12. A method for drilling a pair of wellscomprising: drilling and casing a first fishbone well having a firstplurality of multilateral junctions for a first plurality of lateralwells; and drilling a second fishbone well having a second plurality ofmultilateral junctions for a second plurality of lateral wells, whereindrilling the second fishbone well comprises using magnetic ranging whiledrilling to drill the second plurality of lateral wells above or belowthe first plurality of lateral wells at a controlled distance ofseparation.
 13. The method of claim 12, wherein the controlled distanceof separation is an approximately constant distance of separation. 14.The method of claim 13, wherein drilling the second fishbone wellcomprises using magnetic ranging while drilling to drill the secondplurality of lateral wells above or below the first plurality of wellsat the approximately constant distance of separation, wherein theapproximately constant distance of separation varies by no more than twometers.
 15. The method of claim 12, wherein drilling the first fishbonewell comprises drilling a fishbone producer well, wherein drilling thesecond fishbone well comprises drilling a fishbone injector well, andwherein drilling the second fishbone well comprises using magneticranging while drilling to drill the second plurality of lateral wellsabove the first plurality of lateral wells at the controlled distance ofseparation.
 16. The method of claim 15, wherein the controlled distanceof separation is an approximately constant distance of separation. 17.The method of claim 15, comprising installing a steam generator in thefishbone injector well.
 18. The method of 15, wherein drilling thesecond fishbone well comprises using magnetic ranging while drilling todrill a mother wellbore for the second fishbone well at the controlleddistance of separation from a mother wellbore for the first fishbonewell.
 19. A method of drilling a multilateral well comprising: drillingand casing a mother wellbore; installing at least one multilateraljunction in the mother wellbore; drilling and casing a plurality ofwells of a first type, wherein each of the plurality of wells of thefirst type corresponds respectively to each of a plurality of wells of asecond type; drilling a first of the plurality of wells of the secondtype, wherein drilling the first of the plurality of wells of the secondtype comprises maintaining a controlled distance of separation betweenthe first of the plurality of wells of the second type and a first ofthe plurality of wells of the first type using magnetic ranging whiledrilling; drilling a second of the plurality of wells of the secondtype, wherein drilling the second of the plurality of wells of thesecond type comprises maintaining a controlled distance of separationbetween the second of the plurality of wells of the second type and asecond of the plurality of wells of the first type using magneticranging while drilling.
 20. The method of claim 19, comprising setting awhipstock for the first of the plurality of wells of the second type,wherein setting the whipstock for the first of the plurality of wells ofthe second type is performed after drilling and casing the plurality ofwells of the first type and before drilling the first of the pluralityof wells of the second type.
 21. The method of claim 19, comprisingsetting the whipstock for the second of the plurality of wells of thesecond type, wherein setting the whipstock for the second of theplurality of wells of the second type is performed after drilling andcasing the plurality of wells of the first type and before drilling thesecond of the plurality of wells of the second type.
 22. The method ofclaim 19, wherein the wells of the first type are producer wells and thewells of the second type are injector wells.
 23. The method of claim 22,comprising installing a steam generator in each of the plurality ofinjector wells.
 24. The method of claim 19, wherein the wells of thefirst type are injector wells and the wells of the second type areproducer wells.
 25. The method of claim 24, comprising installing asteam generator in each of the plurality of injector wells.
 26. Themethod of claim 19, wherein the wells of the first type are producerwells and the wells of the second type are monitoring wells.
 27. Themethod of claim 19, wherein the wells of the first type are monitoringwells and the wells of the second type are producer wells.
 28. Themethod of claim 19, wherein the method is performed in the recitedorder.
 29. A method of drilling a multilateral well comprising: drillingand casing a mother wellbore; installing a multilateral junction in themother wellbore; drilling and casing a first lateral well from themultilateral junction, wherein the first lateral well has a length of atleast 500 meters; and drilling a second lateral well from themultilateral junction, wherein drilling the second lateral wellcomprises maintaining a separation distance from the first lateral wellhaving a variance of no greater than two meters over a length of atleast 500 meters.
 30. The method of claim 29, wherein drilling andcasing the first lateral well comprises drilling and casing the firstlateral well, wherein the first lateral well has a length of at least1000 meters, and wherein drilling the second lateral comprisesmaintaining the separation distance having a variance of no greater thantwo meters over a length of at least 1000 meters.
 31. The method ofclaim 29, wherein drilling and casing the first lateral well comprisesdrilling and casing the first lateral well, wherein the first lateralwell has a length of at least 1500 meters, and wherein drilling thesecond lateral comprises maintaining the separation distance having avariance of no greater than two meters over a length of at least 1500meters.
 32. The method of claim 29, wherein drilling the second lateralwell comprises using magnetic ranging while drilling to maintain theseparation distance.
 33. A multilateral well comprising: a motherwellbore; a multilateral junction installed on the mother wellbore; afirst lateral well extending from the multilateral junction; and asecond lateral well extending from the multilateral junction anddisposed at an approximately constant distance of separation from thefirst lateral well.
 34. A multilateral well comprising: a motherwellbore; a multilateral junction installed on the mother wellbore; afirst lateral well extending from the multilateral junction and cased inconductive casing; and a second lateral well extending from themultilateral junction approximately parallel to the first lateral welland disposed at an approximately constant distance of separation fromthe first lateral well, wherein the second lateral well includes abottom hole assembly (BHA) having an electric current driving tool and adrill collar divided by an insulated gap.